In this project the specific objectives are to define the unique epidemiologic, clinical, virologic, and immunologic features of HIV infection in developing countries, to determine the viral kinetics associated with perinatal and heterosexual transmission, and to characterize the molecular strains of HIV throughout the world for infectiousness and progression of disease. We have established population based cohorts in Uganda, South Africa, India, China and the U.S. In one cohort in Rakai, Uganda, 788 HIV-discordant couples have been identified, of whom 253 (31.1%) have transmitted infection during a 10-year period. HIV viral load was the most significant determinant of transmission. Other factors that enhanced transmission were younger age, presence of genital ulcer disease, early or acute HIV infection and lack of circumcision in the men. Co-infection with HSV-2 increased HIV viral load in dually infected individuals and enhanced HIV susceptibility in the uninfected individual. HIV viral loads were determined for 256 subjects with early (incident) HIV infection and for 1,293 subjects with later (prevalent) HIV infection. Viremia was higher after seroconversion than in latency and increased with more advanced disease. We recently performed a retrospective analysis to determine the effect of male circumcision on female HIV and STI acquisition. The incidence of female acquisition was significantly lower in the wives of circumcised HIV-positive men compared to the wives of HIV-positive uncircumcised men. Similarly, the risk of acquiring a STI in female partners of circumcised vs. uncircumcised men was significantly lower for HSV-2, trichomonas, bacterial vaginosis, and genital ulcer disease. Male circumcision may affect male HIV infectivity by removal of foreskin mucosa, thus reducing female HIV exposure, and/or an indirect effect via reduction of female STIs and genital ulcer disease. Depending on the results of ongoing, randomized trials, circumcision may have an important role in preventing the transmission of HIV and STIs in males and in their female partners. We further documented that HIV acquisition is significantly higher during pregnancy than in the post-partum period. We assessed 2,188 HIV-negative, sexually active women with 2,625 pregnant women, 2,887 breast-feeding women, and 8,473 non-pregnant, non-lactating women. HIV incidence was 2.3 per 100 person/year during pregnancy, 1.3 during breast-feeding, and 1.1 in the non-pregnant, non-lactating women. While the risk of HIV acquisition rises during pregnancy, it could not be attributed to sexual risk behaviors but rather may be more related to hormonal changes affecting genital tract mucosa and/or immune response to HIV. HIV prevention efforts are needed during pregnancy to protect the mothers and their infants. In a nested, case-control study in hospitalized children with measles, we examined whether HIV infection was a risk factor for incomplete immunization with DTP and oral polio vaccine (OPV). Of 473 children 23% were incompletely immunized and 19% were HIV infected. HIV-1 infection was significantly associated with incomplete immunization with both vaccines. These findings suggest that HIV-infected children are at increased risk of vaccine-preventable diseases not only because of impaired immune responses but because of lower rates of vaccine coverage.[unreadable] To document viral transmission among partners, molecular sequencing of HIV was performed in samples from 419 HIV-infected individuals, including 84 transmission pairs. Of the 84 transmission pairs, 86% were infected by their sexual partner as indicated by sequence matches. For individuals who reported a monogamous relationship, viral sequences matched in 92% compared to non-monogamous relationships where transmission linkage occurred in 68%. Co-receptor tropism was determined in 108 monogamous couples and we found that subtype A samples were all exclusively CCR5-tropic, subtype D samples (24.6%) were dual CCR5/CXCR4-tropic, and the recombinants were 14.3% dually tropic. In transmission studies, CCR5-tropic viruses transmitted preferentially, but developed CXCR4 tropism early in subtype D infections. In order to determine the effect of HIV subtype on disease progression, we analyzed 567 HIV-infected individuals with known times of infection. Over a follow-up period of five years, 29% of subtype A-infected individuals had progressed to AIDS (CD4 < 200), but none had died. This differed significantly from the subtype D-infected individuals among whom13% had died and 44% developed AIDS. When controlling for the effects of HIV viral load, subtype D and recombinant subtypes (A-D) were significantly more pathogenic than subtype A (p < 0.01). In a cohort of 227 HIV seroconverters followed over two years, 5.9% of subtype D and 4.1% of recombinant-infected individuals died within 24 months whereas none of the 34 subtype A-infected individuals or eight multiply infected individuals had died. In subsequent analyses, CXCR4 phenotype was present in 24% of the subtype D samples, 14% of recombinants, and 0% of subtype A-infected individuals. 15% of HIV seroconverters infected with subtype D develop the X4 phenotype tropism within one year. In summary, viral load has a significant effect on disease progression over a long period of time but only subtype D and recombinant strains incorporating subtype D were found to be more pathogenic than subtype A and predictive of a rapid progression, which was associated with appearance of the CXCR4 coreceptor tropism. In Kampala, Uganda, we evaluated the adherence and treatment outcomes in patients on self-pay for ARV therapy. Overall adherence ranged from 82 to 95% and median CD4 cell count rose by 116 cells within 24 weeks. 72% had undetectable viral loads at 24 weeks. Adherence was associated with viral load suppression, CD4 cell increase, and with improved survival within the first year. ARV resistance was observed in 5% of individuals and was associated with treatment interruption of more than 48 hours. Overall survival was 90%. Adherence is an important predictor of survival with full viral suppression and treatment interruptions important predictors of drug resistance. In a cross-sectional, observational study of 137 HIV-infected individuals in Kampala, Uganda, 66% had undetectable viral load at one year of follow-up. A history of unplanned treatment interruption was associated with virologic treatment failure. The most common genetic mutation was K103N, found in 14 of 27 patients with virologic treatment failure. Although many HIV-infected people have advanced HIV disease, a majority of patients benefited from antiretroviral therapy, experienced viral suppression and clinical benefit. In resource-limited settings, initiation of therapy with a potent, durable regimen accompanied by stable drug supplies will optimize the likelihood of viral suppression. The significance of these studies is that they provide important epidemiologic, clinical, virologic, and immunologic knowledge of HIV infection in developing countries, which can be utilized for monitoring future trends of the epidemic and developing behavioral and biological interventions to prevent further transmission. [unreadable] Methods: 1. Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to HIV-1 and HIV-2. 2. Western blot assays for IgA and IgG for identification of viral proteins and for screening of patients for antibodies to different components of the AIDS virus. 3. Enumeration of lymphocyte subsets of peripheral blood utilizing single and multiple parameter FACS analysis. 4. Isolation and cryopreservation of cellular components of blood, saliva and cervical secretions for PCR of HIV-1. 5. In vitro cultivation of peripheral blood lymphocytes and other bodily fluids for HIV-1. 6. RNA extraction from a variety of tissues and subsequent molecular sequence analysis of RNA gene amplification and quantification utilizing the techniques of RT-PCR for HIV-1. 7. ELISA assays for the detection of p24 antigen in serum and other bodily fluids, and acid hydrolysis for p24 antigen following disruption of immune complexes. 8. Rapid diagnostic assays for detection of antibody to HIV-1 and HIV-2. 9. Semi-quantification by in vitro infectivity assays for viral chemokine proteins, CCR5 and CXCR4. [unreadable] Goals and Objectives: 1. To define the unique epidemiologic, clinical, virologic, and immunologic features of HIV-1 and HIV-2 infection in developing countries. 2. To study the viral kinetics of HIV-1 in order to determine the effect of viral load on transmission of HIV perinatally; in discordant couples to study heterosexual transmission; and in adults with acute endemic opportunistic infections to determine their effect on activation of CD4+ T- lymphocytes and subsequent viral levels. 3. To characterize HIV viral subtype variability throughout the world in order to compare their infectiousness, natural history of viral evolution related to transmission, and the host immunologic response. 4. To develop and evaluate novel interventions to prevent HIV transmission, including microbicides, treatment of sexually transmitted diseases, and vaccines. [unreadable]